Optical materials have long been recognized as valued additions to security threads used in banknotes. These materials allow for a variety of self-authenticating optical effects while rendering the security thread and thus the banknote more resistant to counterfeiting.
By way of example, U.S. Patent Application Publication No. 2005/0180020 A1 to Steenblik et al. depicts a film material that employs a regular two-dimensional array of non-cylindrical lenses to enlarge micro-images. The film material or structure comprises (a) one or more optical spacers; (b) a regular periodic planar array of image icons positioned on one surface of the optical spacer; and (c) a regular periodic array of lenses positioned on an opposing surface of the optical spacer. The lenses are described as being polygonal base multi-zonal lenses, lenses providing enlarged fields of view over the width of the associated image icons so that the peripheral edges of the associated image icons do not drop out of view, or aspheric lenses having effective base diameters of less than 50 microns. For currency, document and product security applications requiring total film thicknesses of less than 50 microns, this reference teaches that the effective base diameter of the lens must be less than 50 microns, and that the focal length of the lens must be less than 40 microns. The images projected by this film structure reportedly show a number of visual effects including orthoparallactic movement.
These micro-optic film structures, in the form of security strips or threads, are either mounted on a surface of a security document (e.g., banknote), or are partially embedded within the document, with the film structures being visible in clearly defined windows on a surface of the document.
In order to preserve the optical effect of the micro-optic film structure when used on or within a security document, print is applied to opposing surfaces of the document so as to avoid or minimize print in the area of the film structure.
By way of the present invention, it has been discovered that printing in the area of the film structure does not impair the film structure's optical performance, and in fact, can be used to enhance or cancel the images projected by such micro-optic film structures, rendering these devices more visually attractive and thus more effective as a public security feature.
The present invention therefore provides an at least partially transparent micro-optic film structure, which projects one or more first synthetic optical images and optionally one or more second synthetic optical images, wherein the one or more first synthetic optical images are spatially coordinated with (i) one or more static images, (ii) one or more second synthetic optical images, or (iii) a combination of one or more static images and one or more second synthetic optical images.
In one contemplated embodiment, the inventive micro-optic film structure projects one or more first synthetic optical images, which are spatially coordinated with one or more static images, and basically comprises:                (a) one or more polymer film materials;        (b) one or more planar arrangements of primary image icons located on or within a polymer film material; and        (c) one or more planar arrangements of focusing elements or lenses located on either a polymer film material or a planar arrangement of primary image icons,                    wherein, the planar arrangements are configured such that when a planar arrangement of primary image icons is viewed through a planar arrangement of focusing elements or lenses, one or more first synthetic optical images are projected; and                        (d) one or more secondary image icons directly or indirectly superimposed upon or formed through one or more primary image icons and/or one or more focusing elements or lenses,                    wherein, the one or more secondary image icons appear as static images spatially coordinated with the one or more first synthetic optical images projected by the film structure,                        wherein, when the static images are viewed with the one or more first synthetic optical images, the static images visually enhance or cancel the projected images.        
As will be evident to one skilled in the art from the above descriptions, synthetic optical images are images formed and projected by/through a planar arrangement of focusing elements or lenses when the primary (and possibly also secondary) image icons are placed on or within the focal plane(s) of the focusing elements or lenses. As will also be evident from the above descriptions, static images are images resulting from placement of the image icons (e.g., printed information) outside the focal plane(s) of the focusing elements or lenses. As such, while these image icons may be directly viewed, or viewed through the micro-optic film structure, the image icons are not imaged and projected by the film structure's planar arrangement of focusing elements or lenses.
The present invention further provides a security document or label having opposing surfaces and comprising at least one micro-optic film structure, as defined above, partially embedded in and/or mounted on a surface of the security document or label.
In one contemplated embodiment of the inventive security document or label, the secondary image icons are directly superimposed on the primary image icons and/or on the focusing elements of the micro-optic film structure by, for example, printing the secondary image icons directly thereon, the film structure being partially embedded in the security document or label and visible in clearly defined windows on a first or upper surface thereof.
In another contemplated embodiment, the film structure is again partially embedded in the security document or label, the secondary image icons being indirectly superimposed on the primary image icons by, for example, printing the secondary image icons on an opposing second or lower surface of the document or label overlying the embedded film structure. In the alternative, or in addition to the secondary image icons located on the lower surface of the document or label, the secondary image icons may be indirectly and/or directly applied to the focusing elements by, for example, printing the secondary image icons directly on and/or between the windowed regions on the upper surface of the document or label.
The present invention further provides a method for authenticating the micro-optic film structure and security document or label, as defined above, which comprises:                (a) directing a coherent light source (e.g., a laser pointer) at a shallow angle over the planar arrangement of focusing elements or lenses of the micro-optic film structure to project a unique pattern;        (b) detecting the unique projected pattern; and        (c) comparing the detected unique projected pattern to expected patterns.        
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.